The cosmological timescale is the longest imaginable. It covers the entire
extent of the universe - many billions of years. A short first period is
measured in tiny fractions of seconds, but thereafter most things happen
on the scale of billion years. It is used to consider events noticeable
on a universal scale, such as the formation of matter, stars, and
galaxies.

The geologic timescale covers the extent of the existence of Earth, from
about 4600 million years ago to the present day. It is used to consider
the formation and change of the Earth itself, and large-scale changes
in the planet's inhabitants.

Human time periods

The "human" timescale covers the time that humans have existed, usually
taken to be from about 250,000 years ago - when Homo Sapiens began to develop.
It is broadly divided into prehistorical (before history began to be recorded)
and historical periods (when written records began to be kept).